Develop Reference

How to get enum value from string if value doesn't match

I have enum:
public enum Enumz{
FIRST_VALUE(0, "one"),
SECOND_VALUE(1, "two"),
THIRD_VALUE(2, "three")
private int id;
private String name;
}
How can I find enum value if my String value match with enum string name? For example: if I have String = "two" I need to get ENUMZ.SECOND_VALUE.

public enum Enumz {
FIRST_VALUE(0, "one"),
SECOND_VALUE(1, "two"),
THIRD_VALUE(2, "three");
private int id;
private String name;
Enumz(int id, String name) {
this.id = id;
this.name = name;
}
public static Enumz fromString(String text) {
for (Enumz b : Enumz.values()) {
if (b.name.equalsIgnoreCase(text)) {
return b;
}
}
return null;
}
}
class Sample{
public static void main(String[] args) {
System.out.println(Enumz.fromString("two"));
}
}
You can implement your own method inside enum and call that method every time you want enum using String.
Above code will printing an output as below
OUTPUT
SECOND_VALUE

You can use Java 8 stream alternative to for loop
String serachValue = "two";
Enumz enumz = Arrays.stream(Enumz.values())
.filter(v -> serachValue.equalsIgnoreCase(v.name))
.findFirst().orElse(null);
Good practice is always put it as a static method into the ENUM itself as explained by other #Sagar Gangwal.

Converting String to appropriate Java object

I have a String in this format (including curly brackets):
{id=123, vehicle_name=Tesla Model X, price=80000.00, ... }
What is the appropriate Java object to represent this String, and how can I convert it to that object?
I would like to be able to query the object to retrieve its values easily, eg. obj.get("vehicle_name"). I've tried converting it to JSON using JSONObject however this expects colons as the delimiters between keys and values, rather than the equals sign.

String itself is a java object.
Parsing String and filling up a java object is not clean.
You can create a java pojo Vehicle with attributeS like id,
vehicle_name etc. Assuming your String will always follow a same
pattern.
Parse the String, and fill this Vehicle pojo.
Below is just a simple example, on how to do it :-
public class Test {
public static void main(String[] args){
String text="{id=123, vehicle_name=Tesla Model X, price=80000.00}";
text=text.replaceAll("[{}]", "");
String[] commaDelimitArray=text.split(",");
Vehicle vehicle=new Vehicle();
for(int i=0;i<commaDelimitArray.length;i++){
String[] keyValuePair=commaDelimitArray[i].split("=");
String key=keyValuePair[0].trim();
String value=keyValuePair[1].trim();
if("id".equals(key)){
vehicle.setId(value);
}
else if("vehicle_name".equals(key)){
vehicle.setVehicleName(value);
}
else if("price".equals(key)){
vehicle.setPrice(value);
}
}
System.out.println(vehicle.getId()+" |"+vehicle.getVehicleName());
}
static class Vehicle{
private String id;
private String vehicleName;
private String price;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getVehicleName() {
return vehicleName;
}
public void setVehicleName(String vehicleName) {
this.vehicleName = vehicleName;
}
public String getPrice() {
return price;
}
public void setPrice(String price) {
this.price = price;
}
}
}

This appears to be an assignment in creating Object classes. If so, you want to create something like this:
public class Car {
int id;
String name;
double price;
//include any other necessary variables
public Car(int id, String name, double price) {
this.id = id;
this.name = name;
this.price = price;
//include any other variables in constructor header and body
}
public void setID(int newID) {
id = newID;
}
public int getID() {
return id;
}
//add getters and setters for other variables in this same manner
}
Note that you could alternatively create a constructor that takes no parameters and initializes variables to default values, then set the values individually using the setter methods.
In your main class, what you want to do is extract the appropriate substrings from your String to pass to the constructor (or setters). There are various ways of doing this (you can read about some ways here); I would personally recommend using regular expressions and a Matcher.

If I had such a string which needed to be converted to an object I would create a class with a static method which returns a Vehicle object. Then you can do whatever you want with that object. A few getters and setters and you should be good to go.
I have come up with some code which should work as you expect if I have understood your question :)
There is quite a few comments so this should help you understand the code logic.
The Vehicle Class is where all parsing happens in the static method named createVehicle(String keyValueString).
The main class:
import java.util.ArrayList;
import java.util.List;
public class main {
public static void main(String[] args) {
String vehicleString = "{id=123, vehicle_name=Tesla Model X, price=80000.00}";
List<Vehicle> vehicles = new ArrayList<Vehicle>();
Vehicle vehicle;
// call the static method passing the string for one vehicle
vehicle = Vehicle.createVehicle(vehicleString);
// if the id is -1, then the default constructor fired since
// there was an error when parsing the code.
if(vehicle.getId() == -1 ) {
System.out.println("Check your data buddy.");
} else {
vehicles.add(vehicle);
}
for(Vehicle v : vehicles){
System.out.println("Vehicle id: " + v.getId());
System.out.println("Vehicle name: " + v.getVehicle_name());
System.out.println("Vehicle price: " + v.getPrice());
System.out.println();
}
}
}
The Vehicle Class:
import java.math.BigDecimal;
public class Vehicle {
// declare your attributes mapped to your string
private int id;
private String vehicle_name;
private BigDecimal price;
// Start Constructor
// Default Constructor
public Vehicle() {
this.setId(-1);
this.setVehicle_name("Empty");
this.setPrice(new BigDecimal(0.00));
}
public Vehicle(int id, String vehicle_name, BigDecimal price) {
this.setId(id);
this.setVehicle_name(vehicle_name);
this.setPrice(price);
}
// End Constructor
// Start Getters and Setters
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getVehicle_name() {
return vehicle_name;
}
public void setVehicle_name(String vehicle_name) {
this.vehicle_name = vehicle_name;
}
public BigDecimal getPrice() {
return price;
}
public void setPrice(BigDecimal price) {
this.price = price;
}
// End Getters and Setters.
// Start Methods and Functions
// Given a string returns a string array split by a "," and with
// "{}" removed.
private static String[] splitString(String keyValueString) {
String[] split;
// Clean string from unwanted values
keyValueString = keyValueString.replaceAll("[{}]", "");
split = keyValueString.split(",");
return split;
}
// Add a vehicle given a formatted string with key value pairs
public static Vehicle createVehicle(String keyValueString) {
int id = 0;
String vehicle_name = "";
BigDecimal price = null;
String[] split;
Vehicle vehicle;
split = splitString(keyValueString);
// Loop through each keyValue array
for(String keyValueJoined : split){
// split the keyValue again using the "="
String[] keyValue = keyValueJoined.split("=");
// remove white space and add to a String variable
String key = keyValue[0].trim();
String value = keyValue[1].trim();
// check which attribute you currently have and add
// to the appropriate variable
switch(key){
case "id":
id = Integer.parseInt(value);
break;
case "vehicle_name":
vehicle_name = value;
break;
case "price":
try {
price = new BigDecimal(Double.parseDouble(value));
} catch (NumberFormatException e) {
e.printStackTrace();
}
break;
default:
System.out.println("Attribute not available");
return null;
}
}
// if any of the values have not been changed then either the
// data is incomplete or inconsistent so return the default constructor.
// Can be removed or changed if you expected incomplete data. It all
// depends how you would like to handle this.
if(id == 0 || vehicle_name.equals("") || price == null){
vehicle = new Vehicle();
} else {
//System.out.println(id);
vehicle = new Vehicle(id, vehicle_name, price);
}
return vehicle;
}
// End Methods and Functions
}
The program, given the string provided, returns the following when accessing the newly created object attributes using the getters:
Vehicle id: 123 Vehicle name: Tesla Model X Vehicle
price: 80000
Hope this helps.

Creating an object and calling it

this is my current code to store rooms(it compiles fine) but in the UML there is a variable called addEquipment and there is also another class called Equipment to be defined. I'm having trouble wrapping my head around what I'm supposed to do with this. Am I supposed to create and call an object called Equipment? what goes in addEquipment?
public class Room {
//begin variable listing
private String name;
private int id;
private int capacity;
private String equipmentList;
//begins get methods for variables
public String getName(){
return name;
}
public int getID(){
return id;
}
public int getCapacity(){
return capacity;
}
public String getEquipmentList(){
return equipmentList;
}
// Set the variables
public void setName(String aName){
name=aName;
}
public void setID(int anID){
id=anID;
}
public void setCapacity(int aCapacity){
capacity=aCapacity;
}
public void setEquipmentList(String anEquipmentList){
equipmentList=anEquipmentList;
}
public String addEquipment(String newEquipment, String currentEquipment){
}
//Create room object
public Room(int capacity, String equipmentList) {
setCapacity(capacity);
setEquipmentList(equipmentList);
}
//Convert variables to string version of room
public String toString(){
return "Room "+name+", capacity: "+capacity+", equipment: "+getEquipmentList();
}
}

You can create a new class Equipment and modify your attribute equipmentList to be a List:
public class Equipment {
private String name;
public Equipment(String name) {
this.name = name;
}
}
public class Room {
//begin variable listing
private String name;
private int id;
private int capacity;
private List<Equipment> equipmentList = new ArrayList<Equipment>();
//begins get methods for variables
public String getName(){
return name;
}
public int getID(){
return id;
}
public int getCapacity(){
return capacity;
}
public List<Equipment> getEquipmentList(){
return equipmentList;
}
// Set the variables
public void setName(String aName){
name=aName;
}
public void setID(int anID){
id=anID;
}
public void setCapacity(int aCapacity){
capacity=aCapacity;
}
public void setEquipmentList(List<Equipment> anEquipmentList){
equipmentList=anEquipmentList;
}
public String addEquipment(String newEquipment, String currentEquipment){
Equipment oneEquipment = new Equipment(newEquipment);
equipmentList.add(oneEquipment);
}
//Create room object
public Room() {
setCapacity(capacity);
setEquipmentList(equipmentList);
}
//Convert variables to string version of room
public String toString(){
String capacity=String.valueOf(getCapacity());
String room = "Room "+name+", capacity: "+capacity+", equipment: "+getEquipmentList();
return room;
}
}
In the method addEquipment, you can create a new Equipment and add it to equipmentList, like code above.

An Equipment class could be anything. Lets assume the "Equipment"-class has a String called "name" as it's attribute
public class Equipment {
String name;
public Equipment( String name) {
this.name = name;
}
public String getName() {
return this.name
}
}
When you extend your Room class by the requested "addEquipment" method, you can do something like this.
public class Room {
... // Your code
private int equipmentIndex = 0;
private Equipment[] equipment = new Equipment[10]; // hold 10 Equipment objects
public void addEquipment( Equipment eq ) {
if ( equipmentIndex < 10 ) {
equipment[ equipmentIndex ] = eq;
equipmentIndex++;
System.out.println("Added new equipment: " + eq.getName());
} else {
System.out.println("The equipment " + eq.getName() + " was not added (array is full)");
}
}
}
Now when you call
room.addEquipment( new Equipment("Chair") );
on your previously initialized object of the Room-class, you will get
"Added new equipment: Chair"
Hope this helps a bit.
PS: The code is untestet (maybe there hides a syntax error somewhere)

Refactoring Java class with multiple responsibilities

public class MyObject
{
public static enum Type {A, B, C, D;}
public static final int ID_MAIN = 1;
public static final int ID_MAIN_UK = 2;
public static final int ID_MAIN_US = 3;
public static final int ID_SUB = 4;
// lots more constants here
public static final String DESCRIPTION_1 = "Desc Full Name";
public static final String DESCRIPTION_2 = "Desc2 Full Name";
// lots more constants here
private int id;
public MyObject(final int id)
{
this.id = id;
}
//simple getter
public int getID() { return this.id;}
// real responsibility of the class is in the following two methods
public static String getDescription()
{
switch(id)
{
case MyObject.ID_MAIN:
case MyObject.ID_MAIN_UK:
return MyObject.DESCRIPTION_1;
case MyObject.ID_SUB:
return MyObject_Description_2;
default:
// throw IllegalArgException
}
}
public static Type getType(int id)
{
switch(id)
{
case MyObject.ID_MAIN:
case MyObject.ID_SUB:
return Type.A;
case MyObject.ID_MAIN_UK:
case MyObject.ID_MAIN_US:
return Type.B;
default:
return Type.Undefined;
}
}
}
Basically, there is an ID that maps to both a description and a type. This ID is passed in during construction of the class and it should map to a set of constants already contained in the class. If the id is not part of the list of constants, an error is thrown when trying to get the description that maps to the id and an 'Unknown' type is return if the type is queried. The ID maps a description to a set of constants. The same ID maps to a certain Type (defined as an enum).
This code is pretty ugly because there are tons of constants defined at the top, which makes the switch statements pretty bloated. Is there a simple way to refactor this without changing the public interface? It seems trivially simple, but it seems pretty ugly no matter how you slice it. How can I simplify these mappings to make the code more concise?
I was thinking about representing the mappings in a text file and having a manager class that held simple containers in a hashmap. When the manager class is constructed, it would create the objects by reading the text file and map them to an ID. When the manager is queried with the ID, it would just call the corresponding get method, for instance:
class Manager
{
private HashMap<int, MyObject> objectMap;
public Manager() {} //construct the object map
public String getDescription(int id) { return objectMap.get(id).getDescription();}
public Type getType(int id) { return objectMap.get(id).getType();}
}
class DataContainer
{
private String description;
private Type type;
public DataContainer(String desc, Type type) {//set mem vars}
public String getDescription() //simple getter
public Type getType() //simple getter
}
But this solution seems too complicated. Is there a better solution, preferably one that would keep everything in one class?

You can do something like following. This would be much cleaner and manageable.
public enum Type
{
MAIN(1, "Main Description"),
MAIN_UK(2, "Main UK Description"),
//....
//Define all the types
//....
UNKNOWN(-1, "Unknown Type");
private int id;
private String description;
private Type(int id, String description)
{
this.id = id;
this.description = description;
}
public static Type getById(int id)
{
for (Type type : Type.values())
{
if (id == type.getId())
{
return type;
}
}
return Type.UNKNOWN;
}
public final int getId()
{
return id;
}
public final String getDescription()
{
return description;
}
}
public class MyObject
{
private int id;
private Type type;
public MyObject(int id)
{
this.id = id;
this.type = Type.getById(id);
}
public int getId()
{
return id;
}
public Type getType()
{
return type;
}
public String getDescription()
{
return type.getDescription();
}
}

In Java enums can have methods. For example following one accepts ID and description and provides some accessors.
public enum Type {
MAIN(1, "desc1"),
UK(2, "desc2"),
SUB(4, "desc4");
private int id;
private String desc;
Type(int id, String desc) {
this.id = id;
this.desc = desc;
}
public String getDescription() {
return desc;
}
public int getType() {
//return id;
return 1+2 + 3+ id;
}
}
You could use that to improve design.

new to java constructor help needed

I have an past exam question that says:
"Create a class Element that records the name of the element as a String and has a public method, toString that returns the String name. Define a constructor for the class (that should receive a String to initialise the name)."
I gave it a go and don't where to go from here...
main class is:
public class builder {
public static void main(String[] args) {
element builderObject = new element(elementName);
}
}
and constructor is:
import java.util.*;
class element {
public int getInt(String[] args) {
Scanner scan = new Scanner(System.in);
System.out.println("Enter the first number");
String elementName = scan.nextLine();
System.out.println("%s");
}
public String toString() {
return elementName;
}
}

Don't get frustrated. Please read java tutorials first and understand the concepts. your exam question is very clear on what you need to do. Atleast for this question, you need to know what is constructor, the purpose of having toString() in a class.
May be the below can help you.
public class Element {
private String elementName;
public Element(String elementName) {
this.elementName = elementName;
}
#Override
public String toString() {
return elementName;
}
}

I can't think of a way to explain this without actually giving the answer, so....
public class Element { /// Create class Element
private final String name; // Record the 'name'
public Element(String name) { // constructor receives and sets the name
this.name = name;
}
public String toString() { // public method toString() returns the name
return name;
}
}

You are missing the constructor itself. The point of constructors is to initialize the object, usually by saving the given parameters to data members.
E.g.:
class Element {
/** A data member to save the Element's name */
private String elementName;
/** A constructor from an Element's name*/
public Element(String elementName) {
this.elementName = elementName;
}
#Override
public String toString() {
return elementName;
}
}

class Element {
private String name = "";
/**
/* Constructor
/**/
public void Element(final String name){
this.name = name;
}
#Override
public String toString(){
return name;
}
}

You don't have a constructor in there. A constructor typically looks something like this:
public class MyClass {
private String name;
private int age;
//This here is the constructor:
public MyClass(String name, int age) {
this.name = name;
this.age = age;
}
//here's a toString method just for demonstration
#Override
public String toString() {
return "Hello, my name is " + name + " and I am " + age + " years old!";
}
}
You should be able to use that as a guideline for making your own constructor.

class Element
{
private String name = "UNSET";
public String getName() { return name; }
public Element(String name) {
this.name = name;
}
public String toString() {
return getName();
}
}

You are missing a constructor you might be looking for something like this
public class Element{
private String name;
public Element(String name){ //Constructor is a method, having same name as class
this.name = name;
}
public String toString(){
return name;
}
}
A note
I take you are starting with java, In java class names usually start with capital letter, thus element should be Element. Its important that one picks up good habits early..